Ion implantation is a process of depositing chemical species into a substrate by direct bombardment of the substrate with energized ions. In semiconductor manufacturing, ion implanters are used primarily for doping processes that alter a type and level of conductivity of target materials. A precise doping profile in an integrated circuit (IC) substrate and its thin-film structure is often crucial for proper IC performance. To achieve a desired doping profile, one or more ion species may be implanted in different doses and at different energy levels.
FIG. 1 depicts a conventional ion implanter system 100. The ion implanter 100 includes a source power 101, an ion source 102, extraction electrodes 104, a 90° magnet analyzer 106, a first deceleration (D1) stage 108, a 70° magnet analyzer 110, and a second deceleration (D2) stage 112. The D1 and D2 deceleration stages (also known as “deceleration lenses”) each comprising multiple electrodes with a defined aperture to allow an ion beam 10 to pass therethrough. By applying different combinations of voltage potentials to the multiple electrodes, the D1 and D2 deceleration lenses can manipulate ion energies and cause the ion beam 10 to hit a target workpiece 114 at a desired energy. A number of measurement devices 116 (e.g., a dose control Faraday cup, a traveling Faraday cup, or a setup Faraday cup) may be used to monitor and control the ion beam conditions.
The ion source 102 and extraction electrodes 104 are critical components of the ion implanter system 100. The ion source 102 and extraction electrodes 104 are required to generate a stable and reliable ion beam 10 for a variety of different ion species and extraction voltages.
FIG. 2 depicts a conventional ion source and extraction electrode configuration 200. Referring to FIG. 2, which is a schematic diagram of the conventional ion source and extraction electrode configuration 200, the ion source 102 is provided in a housing 201. The ion source 102 has a faceplate 203, which has an aperture from which the extraction electrodes 104 may extract ions from plasma in the ion source 102. The extraction electrodes 104 include a suppression electrode 205 and a ground electrode 207. As depicted in FIG. 2, the suppression electrode 205 and the ground electrode 207 are often double-slotted with different slot dimensions, large slot for high-energy implant application (e.g., >20 keV), and small slot for low-energy application (e.g., <20 keV).
It should be appreciated that arrows are shown in FIG. 2 to represent vacuum pumping directions. Vacuum pumping, as depicted by the arrows, is required to provide pressure level low enough for stable beam-extraction operation between the suppression electrode 205 and the ground electrode 207 for ion beam extraction.
FIGS. 3A-3B depict a conventional ground electrode 207. FIG. 3A depicts a three-dimensional view 300A of a conventional ground electrode 207. In this example, the ground electrode 207 is double-slotted, having a first slot 309a and a second slot 309b. FIG. 3B depicts a cross-sectional view 300B of the conventional ground electrode 207. The ground electrode 207 has a overall height H, which includes a base height b and a slot height a. The ground electrode 207 also has a base angle α and a slot angle β. In the conventional ground electrode 207, the base height b is greater than the slot height a and the base-to-slot height ratio may be expressed as b/a>1.
A problem that currently exists in conventional ion implantation is that as extraction current from the ion source 102 increases, undesirable beam shape may be observed at the target workpiece 114. This undesirable beam shape may provide “beam wiggles” that ultimately reduce uniformity in the ion beam 10. Although this problem may be associated with plasma instability and/or plasma oscillation inside the ion source 102, the extraction electrodes 104 play a critical role and may add to the problem. For example, mechanical imperfections and high background pressure at the extraction electrodes 104 may greatly amplify the “beam wiggles” and degrade ion beam quality.
FIG. 4 depicts an illustrative graph 400 of an extracted ion beam profile. In this example, a wiggle-shaped extracted ion beam profile 410 is depicted. As depicted in dotted lines, an ideal extracted ion beam profile 420 is provided. Although both the wiggle-shaped extracted ion beam profile 410 and the ideal extracted ion beam profile 420 have similar profiles, the ideal ion beam profile 420 has a smooth profile, which may be transported and tuned as a high quality ion beam at the target.
As described above, “beam wiggles” generated and/or amplified by the extraction electrodes 104 may lead to degraded beam uniformity and poor quality of the ion beam 10 at the target workpiece 114. In order to improve ion beam quality, the “beam wiggles” in the extracted ion beam profile 410 should be reduced to resemble more closely the ideal extracted ion beam profile 420. However, conventional systems and methods do not provide an adequate solution to reduce “beam wiggles” in an extracted ion beam profile.
In view of the foregoing, it may be understood that there are significant problems and shortcomings associated with current ion beam extraction technologies.